You could scale video using AVFoundation and CoreMedia frameworks.
Take a look at the AVMutableCompositionTrack method:
- (void)scaleTimeRange:(CMTimeRange)timeRange toDuration:(CMTime)duration;
Sample:
AVURLAsset* videoAsset = nil; //self.inputAsset;
//create mutable composition
AVMutableComposition *mixComposition = [AVMutableComposition composition];
AVMutableCompositionTrack *compositionVideoTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo
preferredTrackID:kCMPersistentTrackID_Invalid];
NSError *videoInsertError = nil;
BOOL videoInsertResult = [compositionVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, videoAsset.duration)
ofTrack:[[videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0]
atTime:kCMTimeZero
error:&videoInsertError];
if (!videoInsertResult || nil != videoInsertError) {
//handle error
return;
}
//slow down whole video by 2.0
double videoScaleFactor = 2.0;
CMTime videoDuration = videoAsset.duration;
[compositionVideoTrack scaleTimeRange:CMTimeRangeMake(kCMTimeZero, videoDuration)
toDuration:CMTimeMake(videoDuration.value*videoScaleFactor, videoDuration.timescale)];
//export
AVAssetExportSession* assetExport = [[AVAssetExportSession alloc] initWithAsset:mixComposition
presetName:AVAssetExportPresetLowQuality];
(Probably audio track from videoAsset should also be added to mixComposition)